Biomedical subjects

Jorge Kurchan

Publications and source records attributed to Jorge Kurchan.

5 recordsLinked to original sources

PubMed2006

Direct evaluation of large-deviation functions.

We introduce a numerical procedure to evaluate directly the probabilities of large deviations of physical quantities, such as current or density, that are local in time. The large-deviation functions are given in terms of the typical properties of a modified dynamics, and since they no longer involve rare events, can be evaluated efficiently and over a wider ranges of values. We illustrate the method with the current fluctuations of the Totally Asymmetric Exclusion Process and with the work distribution of a driven Lorentz gas.

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PubMed2005

Shear-thickening and entropy-driven reentrance.

We discuss a generic mechanism for shear thickening analogous to entropy-driven phase reentrance. We implement it in the context of nonrelaxational mean-field glassy systems: although very simple, the microscopic models we study present a dynamical phase diagram with second- and first-order stirring-induced jamming transitions leading to intermittency, metastability, and phase coexistence as seen in some experiments. The jammed state is fragile with respect to change in the stirring direction. Our approach provides a direct derivation of a mode-coupling theory of shear thickening.

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PubMed2003

Topological methods for searching barriers and reaction paths.

We present a family of algorithms for the fast determination of reaction paths and barriers in phase space and the computation of the corresponding rates. The method requires that reaction times be large compared to the microscopic time, irrespective of the origin--energetic, entropic, cooperative--of the time scale separation. It lends itself to temperature cycling as in simulated annealing and to activation-relaxation routines. The dynamics is ultimately based on supersymmetry methods used years ago to derive Morse theory. Thus, the formalism automatically incorporates all relevant topological information.

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PubMed2002

Elementary constraints on autocorrelation function scalings.

Elementary algebraic constraints on the form of an autocorrelation function C(t(w)+tau,t(w)) rule out some two-time scalings found in the literature as possible long-time asymptotic forms. The same argument leads to the realization that two usual definitions of many-time scale relaxation for aging systems are not equivalent.

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PubMed2002

Testing the thermodynamic approach to granular matter with a numerical model of a decisive experiment.

Edwards has proposed a thermodynamic description of dense, slowly flowing granular matter, in which the grains (the 'atoms' of the system) interact with inelastic forces and enduring contacts. In Edwards' ensemble-one of the very few generalizations of standard statistical mechanics-thermodynamic quantities are computed as flat averages over configurations in which the grains are static or jammed, leading to a natural definition of configurational temperature. But the approach is not justified from first principles and hence, in the absence of explicit tests of its validity, has not been widely accepted. Here we report a numerical experiment involving a realistic model of slowly sheared granular matter; our results strongly support the thermodynamic description. Considering particles of different sizes in a slowly sheared dense granular system, we extract an effective temperature from a relation connecting their diffusivity and mobility. We then perform an explicit computation to show that the effective temperature measured from this relation coincides with the Edwards configurational temperature. Our approach, which is specifically conceived to be reproducible in the laboratory, may thus render the Edwards temperature accessible to experiments.

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